Data carriers, such as driving licenses, identity cards, membership cards, badges or passes, passports, discount cards, banking cards, money cards, multi-application cards, and other papers of value; and security documents such as bank notes are widely used. Because of the value and importance associated with each of these data carriers, they are often the subject of unauthorized copying and alterations, and forgeries.
To prevent such activities from being carried out on these data carriers, several different types of data carriers have been implemented. One such data carrier is disclosed in U.S. Patent Application No. 2003/0136847, Eckhard Braun, entitled “Method for producing laser-writable data carriers and Data Carrier produced according to this method”. This document discloses a data carrier that includes a laser-markable layer and a uniform transparent optically-variable layer overlapping therewith, at least in certain areas of the laser-markable layer. This optically-variable layer is not easily detached without damaging or destroying the laser-markable layer therebelow. Visually perceptible markings are inscribed in the laser-markable layer with a laser beam. Some of these markings are inscribed with the laser beam irradiated through the optically-variable layer located thereabove. The laser beam is selected such that the optically-variable layer is transparent to the laser radiation and is not altered by the laser irradiation. The laser beam is also not modified by the optically-variable layer. The laser beam intensity is, however, sufficiently strong to produce energy that is absorbed in the laser-markable layer so that the irradiated areas of the laser-markable layer undergo a color change and form visually well perceptible markings. These markings include personal data, such as name, date of birth, address, personnel number, serial number, signature, portrait, national emblems, insignias, logos etc.
The markings produced by laser inscription are dark or black so that the radiation passing through the optically variable layer is largely or completely absorbed. Therefore, the optically variable effect observable in reflected light of the optically variable layer located above the markings is especially evident in the area of the markings, while the optically variable layer hardly appears in the surroundings of the markings, in particular against a light or white background. Although such a data carrier is, to a certain extent, protected against copying, forgery and manipulation, it can nevertheless still be manipulated. Additional markings may be laser inscribed after the legitimate markings have been inscribed. Such additional laser inscribing makes it possible to falsify the portrait or data by adding new features to the legitimate markings.
It is therefore desirable to produce data carriers with elevated protection against forgery and manipulation using a method that is simple and cost effective.